A great many contributions have been made over the years to the art of threaded fasteners in an effort to produce a fastener combination which will prohibit loosening in an application which produces vibration. Many of these fastener designs are based on the concept that interference between the male and female threadforms will produce additional friction to resist rotation in a direction which de-tensions the fastener in its applied condition.
Many of these prior art thread forms are of interest from a scientific standpoint and can be manufactured under laboratory or near laboratory conditions to actually perform their intended functions. However, these threadforms cannot, for the most part, be manufactured in mass production quantities and remain operable in randomly matched class two or better combinations because of the tolerances in thread dimensions which result from the wear of the thread forming apparatus over the useful life thereof. As will be known to those skilled in the art, these tolerances are established by national organizations and must be adhered to by responsible fastener manufacturers in order to do business on a practical level.
For example, there is the so-called Dardelet thread in which helical flats are formed at the crest of one element and the mating valley of the other element, the flats being formed so as to lie at a shallow angle of less than 13.degree., preferably 6.degree., known as the "angle of friction." The theory of the Dardelet thread is to the effect that the telescopic frictional engagement of these two flats under tensioned fastener conditions will produce sufficient friction to resist the unlocking rotation which would de-tension the fastener combination. As a practical matter, the angle of the flats are so shallow that the variations in radial dimension which are generally permitted under prevailing manufacturing standards would produce an unacceptable percentage of male/female fastener matches in which no engagement of the flats whatsoever would occur. For tight match-ups the Dardelet threadform is very difficult to turn to full tension and is practically impossible to remove and reuse. In brief, the theory of the Dardelet thread is interesting but not practical in mass production.
A fastener which has been found to be practical in mass production and to achieve my objective of radially immobilizing the male and female fastener elements so that vibration does not initiate detensioning rotation therebetween is shown in my U.S. Pat. No. 4,171,012 "Locking Thread Construction," granted Oct. 16, 1979. In that patent I disclose a nonstandard threadform having a relatively steeply angled helical ramp on one element which is engaged by the crest of the mating thread when fusioned to produce the locking effect.